First acquaintance with CANopen

What is? CANOpen

CANOpen It's located in CAN An application layer protocol on the bus .CAN The bus only specifies the physical layer and the data link layer , With these two layers , Data can be found in CAN On the bus . We will make an agreement with which device we communicate with , Which one? ID What is the , Which byte represents what , But in this way , Each manufacturer's equipment defines its own protocol , It's a mess . If an open , Standardized protocols , Manufacturers follow this agreed standard , Then it is easy for devices to communicate with each other .
CANOpen Protocols are usually divided into user application layer 、 Object dictionary 、 The three parts of communication .

CANOpen agreement

CANOpen It consists of a series of protocols . such as CiA301、CiA401、CiA402 Protocol, etc .
CANOpen The basic agreement is CiA 301 agreement . Each industry has its own equipment sub agreement ,

CANOpen Protocol message classification

NMT Network management message , The role is to manage the network , Switch the state of the node . Generally, it is sent by the master station NMT Network management message .
SDO Service data object message , It is used to set equipment parameters , Or the transmission of some key data . Generally, it is initiated by the master station SDO message , Slave station response SDO message . The slave station can also initiate SDO, The master station responds , For example, the transmission of key data .
PDO Process data object message , The function is to transmit process data of some equipment , Such as transmission temperature , Speed and so on . Both master and slave stations send .
EMCY Emergency message , The function is to transmit equipment fault information . Both master and slave stations send .
SYNC Synchronous message , The function is to synchronize data , Used to synchronize the slave station TPDO data . Generally, it is sent by the master station . For example, from the station TPDO The transmission type is in synchronous mode , When the slave station receives the set number of SYNC After the message , The slave station will send TPDO. This will be elaborated in a subsequent article .
NODE GUARDING Node protection message , The function is that the master station requests the status of the slave station , The master station asks , Slave station response . This model has been phased out , Because it takes up too much CAN Bus network bandwidth .
HeartBeat Heartbeat message , The function is that the device actively sends heartbeat , Show yourself online . Both master and slave stations can send .

CANOpen State machine

CANOpen The nodes include ： initialization 、 Pre operation 、 operation 、 Stop these four states . The state machine can go through NMT Services switch to each other . Here's the picture ：

NMT message

Only CANOpen The master station will send NMT message .NMT The message does not need to be answered , Is the producer consumer model .NMT The message ID Fixed is 0, The data field has two bytes , The first byte is the command , The second byte is Node-ID.Node-ID by 0 Indicates all slave stations . Here's the picture

Node protection message

The master station can monitor the current status of each slave node through the node protection message . The master station periodically sends node protection messages to inquire about the status of the slave station , After receiving the inquiry from the master station, the slave station returns its status to the master node .
The master station sends remote frames , Request the status of the slave station . The data answered by the slave station is only one byte , This byte bit7 Is alternating 0、1 The emergence of .bit0~bit6 Indicates the status of the slave station .
The master request format and the slave response format are shown in the following figure ：

The status word of the slave station response is shown in the figure below ：

The node protection message is 0x700+Node-ID , This Node-ID It's from the station Node-ID, Each node must request and respond once . Node protection takes up too much network bandwidth compared to heartbeat .

Heartbeat message ：

Heartbeat message is the message that the slave node actively sends to the master node . Heartbeat messages are periodic , The master node sets a timeout for each slave node , If the heartbeat message of the slave node is not received when the timeout period expires , The master station will perform corresponding actions on the slave station .

Node online message

The slave station takes the initiative to send the node online message to inform the master station that it has entered the pre operation state from the initial state . The startup message is as follows ：

SYNC Synchronous message

Synchronization message CAN-ID Fixed is 0x80, Data length is 0 or 1. Synchronous message is a producer consumer model , From master station , Synchronize the slave station TPDO.

EMCY Emergency message

When an error occurs inside the device , Trigger the object , The format of emergency message is as follows ：

Emergency message COB-ID Stored in 0x1014 The index , It is generally defined as 0x80+Node-ID.
Emergency message ECC( Emergency error code ) as follows ：

The error register of the emergency message is located at 0x1001 Index .
Production prohibition time of emergency message , Stored in index 0x1015 in , Prevent sending emergency messages all the time , Occupy CAN Bus bandwidth .

SDO message

SDO Is the client server model . By using the indexer index SDO The client can access objects in the device object dictionary .
SDO Generally, the length of the transmitted data does not exceed 4 Bytes , When the data length exceeds 4 Bytes are sent by splitting them into several messages .

SDO Read the message as follows ：

SDO Write the message as follows

If you use SDO Return when reading or writing 0x80 Wrong words , You can query the back of the returned data frame 4 Bytes , after 4 Bytes are called abort code , The cause of the error is known by the abort code . The abort code is as follows ：

About PDO Communication is covered in the next article .